In preparing a in-ground swimming pool for off season "storage", sometimes referred to as "winterizing" the pool, especially in relatively cooler climates, a cover is usually used over the body of water in the pool. This winterizing of the swimming pool is desirable for a variety of reasons, including but not limited to: the prevention of accumulation in the pool of debris, such as leaves and other materials; the prevention of unnecessary evaporation of the pool water; as a safeguard to prevent the falling into the unattended pool of a young child or other person or animal; and generally to protect the swimming pool against the elements. In those swimming pools that employ a stairway that comprises a plurality of steps or a ramp-like swim-out area leading from the pool deck into the shallow end of the pool, as distinguished from those swimming pools that use only a removable ladder for ingress and egress from the pool, the stairway opening must also be covered when winterizing the pool. In the past, the usual practice has been to place a sheet of plywood over the stairwell or other opening and attempt to improvise some arrangement for holding the plywood in place and for securing the pool cover to the edge of the plywood closest to the pool interior or to try to use a larger than necessary cover which extends not only over the swimming pool area but also over the deck and other "contiguous" opening and then to hold the cover in place with weights such as logs, water tubes, sandbags, or other weights. This practice has been largely unsatisfactory; is unsafe, because a child or animal can fall through the well area; is relatively ineffective; and is unsightly. With respect to the use of a plywood sheet as a cover, the plywood weathers and splinters. Also, the connection of the pool cover draped over the pool with the cover positioned over the stairwell, to provide an overall integrated seal has been particularly difficult to accomplish and is prone to separation and substantial leakage between the two covers. For at least these reasons, a need exists for a conveniently adaptable stairwell cover or shield that is effective economical and practical such as that provided by the present invention.